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1.
Bikers Butt occurs when one is riding a bicycle in the rain. The back wheel shoots water straight up into the ass region of the biker, causing a soggy, U-shaped wet spot on the seat of the bikers pants. This causes major discomfort when sitting in class or interacting with other individuals in a social setting.
"Dude, why is your butt so wet?"
"Well, I had to get to class fast, so I rode my bike. Unfortunately, it was raining and I got a mad case of Bikers Butt. I had to sit on my wet ass for a 2 hour lab. It fucking sucked!!"
by zbear25 September 10, 2011
 
2.
bikers butt is the overuse of your butt muscles and joints caused (in the majority) of excessive biking
like tennis elbow and/or golfers elbow, bikers butt is a result of an over exertion of a given muscular area
by Hsquarded September 26, 2009